1. Field of the Invention
The present invention relates generally to an imaging apparatus and particularly to an imaging apparatus having an optical sensor arrangement for determining the amount of toner remaining in a toner cartridge.
2. Description of the Related Art
An imaging apparatus such as a copier, printer, facsimile machine, multifunction device, or the like may include a toner cartridge that is removably mounted within the image forming apparatus having a toner reservoir therein. The toner reservoir may include two separate sections for containing toner, a large upper section that stores the majority of the toner when not in use and a small lower section that contains just enough toner to be used during printing. A mechanism in the toner cartridge signals for the upper section to deliver a fixed amount of toner to the lower section when the supply in the lower section gets low. The number of deliveries of toner to the lower section, i.e., the number of “toner addition cycles” or TAC's, may be counted and tracked.
The toner cartridge may include a “gas gage” to indicate to a user an estimate of the amount of toner remaining in the toner cartridge. The number of TAC's may form the basis for the estimate provided by the gas gage. If the initial toner supply, the amount of toner transferred per TAC and the number of TAC's to date are known, the amount of toner remaining in the upper section of the toner reservoir can be estimated.
One prior art system for tracking the number of TAC's includes a cam attached to the shaft of a paddle in the large upper section of the toner reservoir. A pogo pin included in the image forming apparatus rides on the cam and is biased toward the shaft of the paddle with a spring that connects to a push-button sensor. The pogo pin is in constant contact with the cam. When the cam rotates, the pogo pin is pushed back causing the spring to compress and activate the push-button sensor. The number of sensor activations is then used to determine the number of TAC's.
A problem with this system is that it imparts a force continuously on the cartridge regardless of whether the paddle is rotating. This force varies greatly both in magnitude and direction depending on whether the spring is compressed. This relatively large and widely varying force on the toner cartridge may result in print defects. Accordingly, it will be appreciated that a sensor arrangement is needed to track the number of TAC's and, in particular, a sensor arrangement that imparts a relatively low amount of force on the toner cartridge is desired and, if possible, applying only intermittent force.